It is a common practice in the preparation of commercial office space and the like in new building structures to present the new tenant with a bare "slab" floor and "exterior" walls which bound or describe a relatively large expanse of area which the tenant can then subdivide in a way he chooses. Normally, a ceiling grid covering the entire empty floor space to be subsequently partitioned off is installed between the exterior walls of the space prior to the time that the space is then subsequently partitioned off into smaller roomspaces. Typically, the ceiling grid includes rectangular sections of tile which are supported in a suitable lattice work and which can be dislodged and removed or replaced as may be necessary to gain access to the area above the ceiling grid normally used for heating and cooling conduits, electrical lines and the like.
The ceiling grid is peripherally supported by the exterior wall using a component commonly referred to as a "ceiling angle". The angle is generally transversely L-shaped, having a vertical leg which lies along the exterior wall and a horizontal leg or lip which projects outwardly from the wall into the slab space and carries the grid.
The vertical location of the lip is carefully determined and is normally only partially up the height of the exterior walls.
When the interior partitions are then erected, the common practice is to use sections of dry wall material that are somewhat shorter than the ceiling height to thereby leave a small gap between the upper marginal edge of the partitions and the ceiling. Present practice is to thereafter conceal the gap with a piece of trim or molding material known as "L-bead" in such a way that, after being inverted, the transversely L-shaped bead is essentially "hooked over" the upper edge of the partition. In such position the bead is butted up against the underside of the ceiling and is thereupon lightly secured in place on the face of the partition by stapling or the like. Thereafter, the finisher applies a layer of mortar over the L-bead where it lies against the face of the partition so that the L-bead will be fully concealed and the mortar will provide a more suitable, uniform surface for receiving paint or other wall treatment.
It is in the application of mortar to the L-bead, however, that problems can and do arise. First, the mortar is difficult to control perfectly, even by the most skilled finisher. Thus, unless the finisher exercises extreme, painstaking care as he trowels on the mortar, some of it will slip up onto the white ceiling tile and result in an unsightliness that is quite objectionable. Moreover, once the mortar has adhered to the porous, rough surface of the ceiling tile, it is extremely difficult to eradicate and restore the tile to its original, pristine condition.
Therefore, one commonly used technique is for the finisher to loosen the tiles from their supporting grid and to temporarily raise them up away from the underlying L-bead to provide a margin of error for the mortar application. This is an extremely awkward, laborious and time-consuming process, however, and requires the finisher to either somehow raise each tile section with one hand as he attempts to apply mortar with the other hand, or to prop up the tile sections in advance with pieces of scrap lumber or the like which he can scavenge at the construction site. Once the mortar has cured, the finisher must then take the time to remove the props from the raised tile pieces and to properly reset them in place. Obviously, devoting this much time to propping up the tiles, setting them back in place, and then cleaning them off if a mistake is made, makes the current dry wall finishing practice extremely expensive, compared to its cost if those extra steps were not necessary.